MFC r293783: futimens/utimensat: Use the new system calls.

Update the __FreeBSD_version check in lib/libc/sys/futimens.c and
lib/libc/sys/utimensat.c. Before this, fallback code using
futimes/futimesat/lutimes was used except when running on a sufficiently
recent 11-current kernel.

Also, update the history section in the man page.